1. Field of the Invention
This invention relates to a driving method of a matrix display system plasma display panel.
2. Description of Related Art
An AC (alternating current discharge) type plasma display is known as one of display panels of a matrix display scheme.
Such a plasma display panel includes a plurality of row electrodes each bearing a role of a display line, and a plurality of column electrodes so arranged respectively as to intersect the row electrodes. These row and column electrodes are arranged in such a way as to oppose one another while interposing therebetween a discharge space filled with a discharge gas. Discharge cells serving as pixels are formed at the points of intersection between a row electrode pair and the column electrodes inclusive of the discharge space. Since the discharge cell emits light by utilizing a discharge phenomenon, it can assume only two states, that is, a “light emission” state and a “light non-emission” state. In other words, this plasma display device can express luminance of only two gradations, i.e., the lowest luminance (light non-emission state) and the highest luminance (light emission state). Therefore, gradation driving using a sub-field method is executed in order to accomplish luminance display of an intermediate tone corresponding to input image signals for the plasma display panel comprising such discharge cells.
In the driving system using the sub-field method, a display period of one field (frame) is constituted by a plurality of sub-fields. In each sub-field, each of discharge cells is set to either a “light emission cell” state or a “light non-emission cell” state in accordance with pixel data for each pixel on the basis of an input image signal. Only the discharge cell under the “light emission cell” state is allowed to discharge (with light emission) a number of times (for a time) corresponding to weighting of its sub-field, for each sub-field. In this instance, various intermediate luminance can be visually sensed stepwise in accordance with the sum of the number of light emissions made inside the one-field (frame) display period.
In recent years, display apparatus having the plasma display panel mounted thereto have contemplated to increase the number of gradations by combining gradation driving using the sub-field method described above with a multi-gradation processing such as a dither processing.
In such a dither processing, four discharge cells, for example, that are adjacent to one another among the discharge cells arranged in a matrix form are grasped as one discharge cell block. Sequentially, four dither coeffients having different values each are allotted to each of the four discharge cells inside the discharge cell block. Here, a dither coefficient allotted as described above is added to each pixel data corresponding to each discharge cell inside the discharge cell block. Only the high-order bit of the addition result is grasped as new pixel data, and gradation driving described above is executed. According to such a dither processing, new intermediate luminance can be visually sensed depending on the combination of the light emission (or light non-emission) state of the four discharge cells inside the discharge cell block, and the number of gradations can be virtually increased.
According to the multi-gradation method described above, however, a process for adding the dither coefficient to the pixel data is necessary. Therefore, a luminance difference between the adjacent discharge cells greatly fluctuates depending on the value of original pixel data with the result that display quality is likely to drop, too.